1. Field of the Invention
The present invention relates to a micromechanical component as well as to a method for the manufacture thereof.
2. Description of Related Art
Micromechanical sensors frequently use diaphragms which are situated over a cavity. In certain sensors, such as MEMS microphones, the size and shape of this cavity influence the resolution capability of the sensors.
However, not only a MEMS microphone but also a diaphragm sensor is usually implemented, with the aid of a two-step process. A sensor element 120, which includes, for example, a diaphragm and a counter-electrode 130, is placed on a semiconductor substrate 100. As illustrated in FIG. 1a, a cavity 110 which extends to the active sensor structure, i.e., in the case of a microphone, for example to counter-electrode 130, is subsequently introduced into the substrate from rear 170 of semiconductor substrate 100. Cavity 110 may be formed with the aid of a single trench etching process. However, it is necessary for the etch front to very accurately meet the active sensor structure, since a mechanical/acoustic short-circuit could otherwise occur if the cavity opening is offset in relation to the sensor structure. On the other hand, if the cavity opening is designed to be too small in relation to the size of the sensor structure, the sensor structure, for example a diaphragm, is unnecessarily dampened.
In general, a minimum volume must be maintained for the opening beneath the sensor structure, in particular when using a MEMS microphone, to ensure adequate sensitivity. To increase the sensitivity, however, it is desirable to make this volume as large as possible. On the other hand, however, the volume may not be enlarged to any size, since the surface at rear 170 of the component is used to mount the component on p.c. boards or in housings during further processing. A compromise must therefore be found between a large rear volume and an adequately large attachment surface on the rear of the substrate.
FIG. 1b shows a further known example for increasing the rear volume. Compared to the component according to FIG. 1a, a two-phase trench etching process is used in this case. During this procedure, a first trench etching process is used to introduce a cavity 140, having a larger opening compared to active sensor structure 130, into substrate 100. In a subsequent, second trench etching step, a smaller cavity 150 is produced, which is adapted to the dimensions of sensor element 120 or sensor structure 130. Although this process makes it possible to achieve a larger rear volume, including cavities 140 and 150, and thus an increase in sensitivity, the complexity associated with the two separate structuring steps is much higher compared to the component in FIG. 1a. It is also not possible to increase the size of cavity 140 by any amount, since an adequate attachment surface must be provided at rear 170 of substrate 100.
A method which produces a component according to FIG. 1c resolves the dilemma between an increased rear volume and an adequate attachment surface. A ring structure 160 is etched into substrate 100 beneath sensor element 120 or active sensor structure 130, using a combination of anisotropic and isotropic etching steps. This method makes it possible to increase the volume, while maintaining an attachment surface of the same size, compared to FIG. 1a. Due to the ring structure, however, the volume increase thus obtained with regard to the component in FIG. 1a is much smaller than that of the component according to FIG. 1b, maintaining the same thickness of substrate 100.
A method is known from published German patent application document DE 10 2007 026450 A1, in which a side extension of a cavity, may be produced in a semiconductor substrate, using a special trench process.